IAH – Impaired Awareness of Hypoglycemia update 12/2019
Impaired awareness of hypoglycemia (IAH) is defined as a reduced ability to recognize the initial symptoms of hypoglycemia and serves as a risk factor for extreme lows in BG levels in people with insulin treated diabetes.
Some 25% of those dealing with T1D are believed to exhibit this tendency.
Over the past 45 years many procedures for the determination of IAH can be found in the literature. Doctors’ Lablanche and Benhamou who have established diagnostic criteria for distinguishing brittle from stable T1D have selected four of those procedures for inclusion in their list of eight criteria, any two of which, identifies the individual as being brittle.
“A patient will be considered as experiencing a brittle type 1 diabetes if at least two criteria are present among: persistence of severe hypoglycemia, occurrence of ketoacidosis events without obvious etiology, diagnosis of unaware hypoglycemic episodes < 3 mmol/l based on CGM or self-monitoring blood glucose data, a mean blood glucose standard deviation>50%, MAGE index (Mean amplitude of glucose excursions)>60 mg/dl, LBGI index (low blood glucose index)>5, Clarke score≥4 or HYPOSCORE>800.”
The four tests chosen for inclusion are:
Clarke Score – Clarke Score is made up of a series of eight questions characterizing an individual’s exposure to episodes of moderate and severe hypoglycemia to assess the glucose level for and symptomatic response to low blood glucose (LBG) levels. A score of more than or equal to 4 indicates IAH. In essence, Clarke score is used to identify people with T1D who have impaired awareness of hypoglycemia (IAH)
IAH was once thought to have been caused by neuropathy but recent research found that IAH is not associated with autonomic dysfunction or peripheral neuropathy.
This is a composite hypoglycemia score based on the frequency, severity and degree of IAH. It provides a measure of the degree of hypoglycemia together with an assessment of problems with glucose variability and control. The score is developed from an assessment of glucose readings collected from patients over a 4 week period (minimum of two capillary glucose readings a day), noting details of each hypoglycemic event (glucose less than 3.0 mmol/liter), the number of occurrences of hypoglycemia, and a completed questionnaire about the frequency and severity of hypoglycemic episodes over the previous year. In particular, emphasis is placed on which symptoms occur and whether outside help from a third party was obtained to either recognize or treat a hypoglycemic event. A score of >1,000 indicative of severe hypoglycemia. Lablanche and Benhamou have chosen a hyposcore >800 as a determining factor for brittleness.
LBGI predicts the outcome of type1 diabetic patients who switch to continuous subcutaneous insulin infusion (CSII) (pump therapy) in terms of hypoglycemia.
A research paper entitled - Glucose Variability Assessed by Low Blood Glucose Index Is Predictive of Hypoglycemic Events in Patients With Type 1 Diabetes Switched to Pump Therapy – provides a detailed analysis of this procedure.
Calculating the mean amplitude of glycemic excursion from continuous glucose monitoring data: an automated algorithm.
An automated algorithm for identifying the peaks and nadirs (lowest points) corresponding to the glycemic excursions required for the MAGE calculation has been developed. The algorithm takes a column of timed glucose measurements and generates a plot joining the peaks and nadirs required for estimating the MAGE. It returns estimates of the MAGE for both upward and downward excursions, together with several other indices of glycemic variability.
Glycemic variability is discussed in detail here:
Mean Amplitude of Glycemic Excursions, a Measure of Diabetic Instability was first introduced 46 years ago. This is the original paper explaining how the concept works and measurements are made. It was later modified to include an algorithm.